The present invention relates to transparent polymer compounds, particularly to transparent polymer compounds containing fluorine atom in their molecules. Such polymer compounds are useful as a material for plastic optical fibers and optical waveguides, particularly as core, cladding and covering materials of plastic optical fibers and optical wave guides.
In general, fluorine-containing polymer compounds are used for various fields, since they are superior in heat resistance, chemical resistance and electrical characteristics. However, conventional fluorine-containing polymer compounds (e.g., tetrafluoroethylene, vinylidene fluoride and chlorotrifluoroethylene), which are prepared by polymerizing fluorine-containing vinyl monomers, usually contain a crystalline component, making light scattering and thereby causing low transparency. Therefore, such fluorine-containing polymer compounds have almost not been used in an optical field requiring high transparency. However, fluorine-containing polymer compounds themselves are specifically low in refractive index and low in light absorption in a wide wavelength range due to their fluorine atom properties. Therefore, fluorine-containing polymer compounds have a potential for becoming a very useful material in optical fields.
There are several proposals for improving fluorine-containing polymer compounds in transparency. Japanese Patent Laid-open Publication Showa 63-238115 discloses a process for producing a copolymer (containing a cyclic structure in its main chain) by a radical copolymerization between a perfluoroether having an end double bond and another monomer capable of radical copolymerization. The resulting copolymer shows a higher transparency, as compared with conventional fluorine-containing polymer compounds such as polytetrafluoroethylene and polyvinylidene fluoride. Japanese Patent Examined Publication Showa 63-18964, corresponding to EP 0073087A, discloses an amorphous copolymer comprising perfluoro-2,2-dimethyl-1,3-dioxol, tetrafluoroethylene and optionally at least one another ethylene-type unsaturated monomer. However, there still exist needs for such fluorine-containing polymer compounds to have a sufficient solubility in common solvents and to have an improved adhesion to other materials.
Acrylic or methacrylic ester-based polymers are widely used as optical materials. In recent years, there have been proposals for introducing fluorine atom into such polymers and the use of the resulting polymers as optical materials. Polyacrylicfluoroalkylester resins are considered to have acrylic resin properties and fluororesin properties. It is possible to change the fluorine content of such resins by changing the type of the fluoroalkyl group of the monomer (raw material). However, in the case of increasing the fluorine content by using a longer fluoroalkyl side chain, the resulting resins may have a lower glass transition point and a lower adhesion to various substrates. If the fluoroalkyl side chain has a carbon atom number greater than 6, the glass transition point may increase due to the crystallization of this side chain. The resulting resins may become inferior in transparency. As mentioned hereinabove, although it is possible to lower refractive index by introducing many fluorine atoms into an alkyl side chain of the acrylic ester, the resulting resins may become inferior in other properties.
Macromol. Chem. Phys. 196, 2840-2853 (1995) discloses (a) a synthesis of a homopolymer from an α-trifluoromethyl-acrylic acid or α-trifluoromethylacrylic methyl ester; (b) a synthesis of a copolymer by copolymerizing α-trifluoromethyl-acrylic methyl ester and a vinyl ether such as butyl vinyl ether or methyl vinyl ether; and (c) a synthesis of a copolymer by copolymerizing α-trifluoromethylacrylic methyl ester and α-olefin such as 1-decene.
Macromolecules 1982, 15, 915-920 discloses a homopolymer of α-trifluoromethylacrylicmethyl ester, and a copolymer of α-trifluoromethylacrylicmethyl ester and methyl methacrylate.
Japanese Patent Examined Publication Heisei 4-19247, corresponding to U.S. Pat. No. 4,613,657, discloses a production of homopolymers of α-trifluoromethylacrylictrifluoroethyl ester and α-trifluoromethylacrylichexafluoroisopropyl ester by anionic polymerization.